Alcohols find use in a variety of chemical processes. The hydration of alkenes to alcohols, such as the hydration of butene to butanol, is a commercially important reaction as the reaction products find several important industrial applications. For example, butanol can be used as a solvent or chemical intermediate for the productions of corresponding ketones, esters, and ethers, as well as being used for the preparation of a variety of other chemical compounds. In a similar fashion, other low molecular weight alkenes can be converted into corresponding low molecular weight alcohols for use as solvents or intermediates for the production of additional chemical compounds. Additionally, low molecular weight alcohols can also be used as additive or blending components for gasoline.
The hydration of alkenes to alcohols is typically an acid catalyzed reaction. The reaction typically requires relatively strong liquid Bronsted acids to achieve the desired reaction kinetics. Thus, the elimination of the use of strong Bronsted acids in olefin hydration is desirable.
For example, in one commercially practiced method for producing secondary butyl alcohols, a two-step process is employed wherein n-butenes are reacted with excess sulfuric acid (for example, 80%) to form the corresponding sulfate, which is then hydrolysed to sec-butanol, as follows:C4H8+H2SO4→C4H9OSO3H  (1)C4H9OSO3H+H2O→C4H9OH+H2SO4  (2)During this process, the sulfuric acid becomes diluted to a concentration of about 35% by weight or less, and must then be re-concentrated before it can be recycled and used in the process. The process also has additional problems associated with the use of such liquid catalysts. Among these problems includes separation and recovery of the catalyst, corrosion of equipment and installations that come into contact with catalyst, and the formation of undesired byproducts, such as sec-butyl ether, isopropyl alcohol, various C5-C8 hydrocarbons, and polymers. In addition to reducing the overall yield of the reaction, some of these by-products also complicate the purification and recovery of the desired sec-butanol product.
In general, there are no solid acid catalysts suitable for use in the hydration of alcohols in the presence of water, except perhaps for certain ion exchange resins. Cationic exchange resins are known to offer substantial reaction rates in both polar and non-polar media. The use of cationic exchange resins that include sulfonated polystyrene resins cross-linked with divinyl benzene as catalysts for the hydration of olefins, such as propylene or butene, has been previously described in the literature (see, for example, U.S. Pat. Nos. 4,579,984 and 2,477,380; and the references cited therein). These exchange resins are believed to generally offer several process benefits, for example ease in separation of products and a non-corrosive environment. The use of these exchange resins, however, has certain limitations and many have not been found to be entirely satisfactory due, in part, to their leaching tendency, their limited range of application, and a general lack of the ability to regenerate and reuse the media.
Butanols have been identified as second generation biofuel component (i.e., biofuels obtained from non-food crops) after ethanol. The bio-route to produce such butanols, as an alternative to known methods for producing butanols, such as the hydration of olefins, has been previously reported, however, butanols that are produced through the bio-route are not efficient and the amount of butanols produced will not be enough to meet the demand of the butanol market. The production of butanols from propylene and carbon monoxide is costly and typically only produces n-butanol, which has relative low octane value as compared with the other butanol isomers. Thus, an effective and economical route to produce mixed butanols through olefin hydration is needed.
Although the olefin hydration has been studied extensively, one main objective of olefin hydration is to produce a single alcohol molecule, as opposed to a mixture of alcohols, to avoid complications associated with the separation thereof. When alcohols are utilized as fuel components, however, it is unnecessary to separate them out prior to use. Olefin hydration with strong Bronsted acids typically produces mixed alcohols product streams, and thus are useful as fuel components, but are not useful as intermediate chemicals.
As the direct catalytic hydration of alkenes to alcohols is an inexpensive route for preparing industrially useful alcohols, and a convenient synthetic route for the synthesis of secondary and tertiary alcohols in general, it is desirable to obtain solid catalysts for the reaction that are suitable for use in water.